This relates to provision of service and more particularly to an arrangement and a method for delivering service to a specified pair of nodes in a multi-hop contention-based network, with the delivered service having a high quality-of-service (QoS) level.
One contention-based medium access method that is widely used in unstructured wireless communication networks is the Carrier Sense Multiple Access (CSMA) method. For example, both WiFi and Zigbee standards mandate support for some form of CSMA. Characterized by their “flatness,” multi-hop wireless networks, such as mobile ad hoc networks and wireless mesh networks, are often CSMA networks as well.
A transmitter in a CSMA network must determine whether the channel is busy before accessing the communication channel. If the channel is busy, the transmitter refrains from transmitting and attempts to access the channel again at a later time. If the channel is idle, the transmitter may begin its transmission immediately, begin its transmission with a certain probability, or wait another period of time—creating an extended time window—to further reduce probability of collision and only access the channel (i.e., begin transmitting) if the channel remains idle during this extended time window.
CSMA is inherently inefficient in busy networks because nodes effectively waste time in waiting when channel access is found to be unavailable. It has been shown that channel access performance degrades rapidly as network load and node density increase. In addition, the duration and outcome of the contention process are only statistically predictable. Consequently, CSMA is not well suited for delivering data with high QoS requirements, such as low delay and low jitter. The same is true for other contention-based networks.